Hydrostatic Pressure Calculator

A column of fluid of height h presses on its base with its own weight per unit area: p = ρ g h. It depends only on depth and density, not on the shape or width of the container (the hydrostatic paradox). The result is a gauge pressure — above whatever acts on the free surface. The density shown at first is a labelled water sample; enter your fluid's, and note that seawater, brine, oils and slurries differ by several percent or more.

A horizontal surface at depth h sees a uniform pressure, so the force is simply p × A. A vertical wall sees pressure growing linearly from zero at the surface to ρgh at the bottom; the total force on a rectangular wall of width w is the area of that triangle, ρ g w h² ÷ 2, and it acts at the triangle's centroid, two-thirds of the depth below the surface — the centre of pressure. A wall or baffle should be checked for the moment about its base using that point, not mid-depth. Inclined and non-rectangular walls need the general plane-surface formulas and are out of scope.

If the tank is pressurised (or a pump holds pressure on the surface), that pressure adds uniformly at every depth. The page adds it to the column pressure and to both forces, and moves the wall's centre of pressure towards mid-depth accordingly. Everything stays gauge; absolute pressure would add the atmosphere as well.

Metric uses kg/m³, metres, bar and kN; imperial uses lb/ft³, feet, psi and lbf. The conversion table lists Pa, kPa, bar, psi, metres and feet of water (at exactly 1,000 kg/m³) and millimetres of mercury (13,595.1 kg/m³). Nothing leaves the browser; the same four anonymous usage counts as the rest of the site apply.